Right off we can eliminate the Brucci (middle finger). I can see it's a bit lighter than the other two and a bit more pink.

As for the Essie (pointer, ring) and Sinful (pinkie) - I wouldn't say they are EXACT dupe - it looks to me like the Sinful is a tiiiiiiiiiiny tiny bit more saturated, a little more rich. But I'd say that if you have the one, you don't need the other. Considering that the Sinful is only $2 while the Essie is around $8, I'd grab the Sinful and be done with it.

In this case, I'd chance it to say that these two are exact dupes as far as color. They're the exact same shade of pastel green and pretty much indiscernible on the nail. The formula is a different story. I found the American Apparel polish to apply much smoother and much more opaque. You can see how lumpy and streaky my middle and pinkie fingers look with the E.L.F. polish. If you're going for value, I'd grab the E.L.F. as it's only a dollar, and should be fine with a third coat. The AA is only $5 though, and for me would be worth the extra dough for easier application.

Overlooking the shimmer, these are not as close in color as I thought they were. High Society is a bit warmer while Grey Sky leans more toward it's namesake grey shade. Factor in the shimmer and these two are different enough to justify owning both. Lucky for me I love love love my taupe polishes! They're some of my favorite and definitely some of the classiest of my collection.

Hope this was helpful! I'll keep an eye out for any more dupes in my collection :)